Editing Copenhagen interpretation (section)

==Alternatives==
{{Further|Interpretations of quantum mechanics}}
A large number of alternative interpretations have appeared, sharing some aspects of the Copenhagen interpretation while providing alternatives to other aspects. 
The [[ensemble interpretation]] is similar; it offers an interpretation of the wave function, but not for single particles. The [[consistent histories]] interpretation advertises itself as "Copenhagen done right".<ref>{{Cite journal|last=Hohenberg|first=P. C.|author-link=Pierre Hohenberg|date=2010-10-05|title=Colloquium : An introduction to consistent quantum theory|url=https://link.aps.org/doi/10.1103/RevModPhys.82.2835|journal=[[Reviews of Modern Physics]] |language=en|volume=82|issue=4|pages=2835–2844|doi=10.1103/RevModPhys.82.2835|arxiv=0909.2359 |bibcode=2010RvMP...82.2835H |s2cid=20551033 |issn=0034-6861}}</ref> More recently, interpretations inspired by [[quantum information theory]] like [[QBism]]<ref>{{Cite book|last=Healey|first=Richard|title=[[Stanford Encyclopedia of Philosophy]]|publisher=Metaphysics Research Lab, Stanford University|year=2016|editor-last=Zalta|editor-first=Edward N.|chapter=Quantum-Bayesian and Pragmatist Views of Quantum Theory|chapter-url=https://plato.stanford.edu/entries/quantum-bayesian/}}</ref> and [[relational quantum mechanics]]<ref>See, for example:
*{{Cite journal|last=van Fraassen|first=Bas C.|author-link=Bas van Fraassen|date=April 2010|title=Rovelli's World|url=http://link.springer.com/10.1007/s10701-009-9326-5|journal=[[Foundations of Physics]]|language=en|volume=40|issue=4|pages=390–417|doi=10.1007/s10701-009-9326-5|bibcode=2010FoPh...40..390V|s2cid=17217776|issn=0015-9018}}
*{{Cite web|last=Prescod-Weinstein|first=Chanda|author-link=Chanda Prescod-Weinstein|date=2021-07-07|title=No man is an island – the early days of the quantum revolution|url=https://physicsworld.com/no-man-is-an-island/|access-date=2022-02-03|website=[[Physics World]]|language=en-GB |quote=In short, the relational interpretation insists that the quantum state of a system depends on the observer, and it is a concept that Rovelli has helped to formalize and convert into an area of active research.}}</ref> have appeared. Experts on quantum foundational issues continue to favor the Copenhagen interpretation over other alternatives.<ref name=":8" /> Physicists who have suggested that the Copenhagen tradition needs to be built upon or extended include [[Rudolf Haag]] and [[Anton Zeilinger]].<ref name=":4" /><ref>{{Cite journal|last=Zeilinger|first=Anton|author-link=Anton Zeilinger|date=1999|title=A foundational principle for quantum mechanics|url=http://link.springer.com/10.1023/A:1018820410908|journal=[[Foundations of Physics]]|volume=29|issue=4|pages=631–643|doi=10.1023/A:1018820410908|bibcode=1999FoPh...29..631Z |s2cid=16514757 |quote=Suffice it to say here that, in my view, the principle naturally supports and extends the Copenhagen interpretation of quantum mechanics. It is evident that one of the immediate consequences is that in physics we cannot talk about reality independent of what can be said about reality. Likewise it does not make sense to reduce the task of physics to just making subjective statements, because any statements about the physical world must ultimately be subject to experiment. Therefore, while in a classical worldview, reality is a primary concept prior to and independent of observation with all its properties, in the emerging view of quantum mechanics the notions of reality and of information are on an equal footing. One implies the other and neither one is sufficient to obtain a complete understanding of the world.}}</ref>

Under [[Philosophical realism|realism]] and [[determinism]], if the wave function is regarded as ontologically real, and collapse is entirely rejected, a [[many-worlds interpretation]] results. If wave function collapse is regarded as ontologically real as well, an [[objective collapse theory]] is obtained. [[Bohmian mechanics]] shows that it is possible to reformulate quantum mechanics to make it deterministic, at the price of making it explicitly nonlocal. It attributes not only a wave function to a physical system, but in addition a real position, that evolves deterministically under a nonlocal guiding equation. The evolution of a physical system is given at all times by the Schrödinger equation together with the guiding equation; there is never a collapse of the wave function.<ref>{{cite book|chapter-url=https://plato.stanford.edu/entries/qm-bohm/ |last=Goldstein |first=Sheldon |chapter=Bohmian Mechanics |title=[[Stanford Encyclopedia of Philosophy]] |year=2017|publisher=Metaphysics Research Lab, Stanford University }}</ref> The [[transactional interpretation]] is also explicitly nonlocal.<ref name="Kastner2010">{{cite journal|title=The Quantum Liar Experiment in Cramer's transactional interpretation |first=R. E. |last=Kastner |journal=[[Studies in History and Philosophy of Modern Physics]] |volume=41 |number=2 |date=May 2010 |pages=86–92 |doi=10.1016/j.shpsb.2010.01.001|arxiv=0906.1626 |bibcode=2010SHPMP..41...86K |s2cid=16242184 }}</ref>

Some physicists espoused views in the "Copenhagen spirit" and then went on to advocate other interpretations. For example, [[David Bohm]] and [[Alfred Landé]] both wrote textbooks that put forth ideas in the Bohr–Heisenberg tradition, and later promoted nonlocal hidden variables and an [[ensemble interpretation]] respectively.<ref name=":0" />{{rp|453}} [[John Archibald Wheeler]] began his career as an "apostle of Niels Bohr";<ref>{{cite book|first=James |last=Gleick |author-link=James Gleick |title=Genius: The Life and Science of Richard Feynman |year=1992 |publisher=Vintage Books |isbn=978-0-679-74704-8 |oclc=223830601}}</ref> he then supervised the PhD thesis of Hugh Everett that proposed the many-worlds interpretation. After supporting Everett's work for several years, he began to distance himself from the many-worlds interpretation in the 1970s.<ref>{{cite book|first=John Archibald |last=Wheeler |author-link=John Archibald Wheeler |chapter=Include the observer in the wave function? |title=Quantum Mechanics: A Half Century Later |editor-first1=J. Leite |editor-last1=Lopes |editor-first2=M. |editor-last2=Paty |publisher=D. Reidel Publishing |year=1977}}</ref><ref>{{cite book|first=Peter |last=Byrne |title=The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family |publisher=Oxford University Press |year=2012 |isbn=978-0-199-55227-6 |oclc=809554486}}</ref> Late in life, he wrote that while the Copenhagen interpretation might fairly be called "the fog from the north", it "remains the best interpretation of the quantum that we have".<ref>{{cite web|url=https://www.nytimes.com/2000/12/12/science/essay-a-practical-tool-but-puzzling-too.html |title='A Practical Tool,' But Puzzling, Too |first=John Archibald |last=Wheeler |author-link=John Archibald Wheeler |website=[[New York Times]] |date=2000-12-12 |access-date=2020-12-25}}</ref>

Other physicists, while influenced by the Copenhagen tradition, have expressed frustration at how it took the mathematical formalism of quantum theory as given, rather than trying to understand how it might arise from something more fundamental. ([[E. T. Jaynes]] described the mathematical formalism of quantum physics as "a peculiar mixture describing in part realities of Nature, in part incomplete human information about Nature—all scrambled up together by Heisenberg and Bohr into an omelette that nobody has seen how to unscramble".<ref>{{cite book|first=E. T. |last=Jaynes |author-link=E. T. Jaynes |chapter=Probability in Quantum Theory |title=Complexity, Entropy, and the Physics of Information |editor-first=W. H. |editor-last=Zurek |editor-link=Wojciech H. Zurek |publisher=Addison-Wesley |year=1990 |pages=381–404 |isbn=9780201515060 |oclc=946145335}}</ref>) This dissatisfaction has motivated new interpretative variants as well as technical work in [[quantum foundations]].<ref name=":3">{{cite journal|first=D. M. |last=Appleby |title=Facts, Values and Quanta |journal=[[Foundations of Physics]] |volume=35 |page=637 |year=2005 |issue=4 |arxiv=quant-ph/0402015 |doi=10.1007/s10701-004-2014-6 |bibcode=2005FoPh...35..627A|s2cid=16072294 }}</ref><ref>{{cite journal|first=Christopher A. |last=Fuchs |title=Copenhagen Interpretation Delenda Est? |journal=[[American Journal of Physics]] |year=2018 |arxiv=1809.05147 |bibcode=2018arXiv180905147F |doi=10.1119/1.5089208 |volume=87 |number=4 |pages=317–318|s2cid=224755562 }}</ref>